Brexit could leave the Peak District National Park 'struggling to make ends meet', according to pro-EU campaigners.
According to figures obtained under a Freedom of Information Act request, national parks in England have received almost £6.4million from the EU over the last five years, with the Peak District getting the most - £3.6m.
In recent years there have been growing concerns about the decline in Government funding for these sites, with an investigation in 2016 revealing that spending on national parks has been cut by a quarter since 2011.
Mary Creagh MP, chairman of the Environmental Audit Committee, said: "Our beautiful and precious national parks are one of the many things that make Britain great.
"Money from the EU is a vital source of funding for them, without which they would struggle to make ends meet.
"The Peak District alone has received over £3.6m across the last five years, directly from European Commission funding, by far the most of any English national park.
"If that source of funding is lost, the people who work so hard to maintain our national parks would find it much harder to do their jobs effectively.
"No-one voted in the referendum to give less money to national parks or to damage our countryside.
"If the Government cannot guarantee equal or increased levels of funding, people have the right to keep an open mind about our future relationship with Europe."
In response, a Government spokesman said: "National parks are some of our most treasured landscapes and as we work towards a green Brexit we are committed to helping them thrive.
"We have increased their budgets each year since 2015 and by 2020 we will have given our national parks more than £200m in funding."